Calcium fluoride phosphors activated by terbium and europium



April 21, 1970 INTENSITY (relative units) A R. L. AMSTER CALCIUM FLUORIDE PHOSPHORS ACTIVATED BY TERBiUM AND EUROPIUM Filed July INTENSITY (relative units) mooo o WAVELENGTH 500 (nanometers) Fig.

INTENSITY (relative units) WAVELEN GTH (nanometers) Fig. 2.

WAVELENGTH (nanometers) Fig. 3.

INVENTOR.

ROBERT L. AMSTER 3,507,802 CALCIUM FLUORIDE PHOSPHORS ACTIVATED BY TERBIUM AND EUROPIUM Robert L. Amster, Great Neck, N .Y., assignor to General Telephone & Electronics Laboratories Incorporated, a corporation of Delaware Filed July 19, 1967, Ser. No. 654,454 Int. Cl. C09k 1/06 US. Cl. 252301.4 Claims ABSTRACT OF THE DISCLOSURE A phosphor system consisting of calcium fluoride activated by divalent europium and trivalent terbium. These phosphors are photoluminescent and are suitable for use in fluorescent lamps.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to fluorescent materials which emit light in the green region of the spectrum when excited by ultraviolet radiation. In particular, it is related to a series of phosphors comprising calcium fluoride activated by divalent europium and trivalent terbium.

Description of the prior art quite strong, only a weak emission is obtained from eX- citation by the 254 nanometer line.

SUMMARY OF THE INVENTION I have discovered that when divalent europium is added to trivalent terbium activated calcium fluoride the fluorescence intensity of the terbium is greatly enhanced for excitation over the entire 200 to 400 nanometer spectral region. This new phosphor system may be represented by the general formula (Ca Eu Tb Na F where x is a quantity in the range 0.0025 to 0.06, y is a quantity in the range 0.01 to 0.10, z is a quantity in the range 0 to 0.10, and w=1(x+z+y).

Divalent europium has a broad absorption band in the ultraviolet region extending from 200 to 400 nanometers and much of the energy absorbed by the divalent europium is transferred to the trivalent terbium ions which then emit their characteristic fluorescence. Thus, trivalent terbium emission is sensitized by divalent europium. The strong emission in the band centered at 435 nanometers in CaF :Eu is largely suppressed by the addition of terbium.

Material containing no Nan yields a phosphor, CaF :Eu +,Tb having a bright blue-green emission suitable for use in fluorescent lamps. The addition of sodium fluoride to CaF :Eu +,Tb with resultant charge compensation of Tb by the sodium ion, leads to further suppression of the blue Eu emission. Fluorescence from this phosphor, CaF :Eu +,Tb +,Na+, appears more green to the eye than CaF :Eu +,Tb and is also suitable for fluorescent lamp application. Surprisingly, no significant United States Patent 0 T 3,507,802 Patented Apr. 21, 1970 photosensitization of Tb by Eu was found in related hosts such as SrF BaF CaFCl, and BaFBr.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the excitation and emission curves for a prior art phosphor, CaF :Tb

FIG. 2 shows, to the same scale as FIG. 1, the excitation and emission curves for one of the phosphors of the present invention, CaF :Eu +,Tb and FIG. 3 shows the excitation and emission curves for another novel phosphor, CaF :Eu Tb Na+.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I 0.185 gram of powdered EuCl -6 H 0 and 0.210 gram of TbF -0.5 H O were dry blended with 1.0 gram of CaF The blend was placed in an alumina boat and fired in a quartz reaction tube located in a tube furnace preheated to 500 C. The firing was carried out in a hydrogen atmosphere at 1050 C. for approximately two hours. (It has been found that further heating reduces the fluorescent intensity while a shorter firing period results in incomplete incorporation of the activators.) After firing, the reaction tube is removed from the furnace and the product allowed to cool to ambient temperature while in the reducing atmosphere.

The resultant phosphor ca, ,,Eu, ,,'rb, F was excited by radiation in the range 200 to 400 nanometers. Excitation curve A of FIG. 2 was obtained by measuring the intensity of the radiation from the phosphor at 541 nanometers as the excitation wavelength was varied through the 200 to 400 nanometer range. As shown, emission was obtained over a wide range of excitation wave lengths centered at about 360 nanometers. Curve B illustrates the emission obtained from the phosphor when it was excited by radiation having a wavelength of 360 nanometers.

Comparison of the emission curve B of FIG. 2 for (ca Eu Tb gF with that of the prior art phosphor (Ca Tb )F shown at B in FIG. 1 indicates that the peak emission for both materials is obtained at 541 nanometers. However, the peak intensity of Relative intensity Medium pressure Low pressure Phosphor Hg lamp Hg lamp Zn2SiO4:Mn +(standa1d) 29 o.9 0.036 bo.004) 2 100 20 Example II A phosphor was prepared by the method of Example I except that 0.06 gram of NaF were blended with 0.185 gram of EuCl -6H O, 0.210 gram of TbF -0.5H O and 089 gram of CaF The resultant phosphor had a greater intensity of emission at 541 nanometers than the material without sodium and the emission at 435 nanometers corresponding to the Eu emission was nearly completely suppressed. This is shown by the excitation curve A and emission curve B of FIG. 3.

Example III Additional samples were prepared of phosphor compositions having the general formula (Ca Eu 'Ib Na )F in which x was varied between 0.0025 and 0.06, y between 0.01 and 0.10 and z from 0 to 0.10. In all cases, green emitting phosphors were obtained but their intensities were somewhat less than that exhibited by the phosphors of Examples I and II.

What is claimed is:

1. A phosphor composition consisting essentially of calcium fluoride activated by 0.0025 to 0.06 divalent europium and 0.01 to 0.10 trivalent terbium.

2. The phosphor composition defined by claim 1 wherein said trivalent terbium is charge compensated by the addition of sodium.

3. A composition of matter defined by the formula (Ca Eu 'I'b Na )F where Eu is divalent, Tb is trivalent,

x is a quantity in the range 0.0025 to 0.06, y is a quantity in the range 0.01 to 0.10, z is a quantity in the range 0 to 0.10 and w=1(x+y+z).

4. The composition of matter defined by claim 3 wherein x equals approximately 0.036, y equals approximately 0.064, and z equals zero.

5. The composition of matter defined by claim 3 wherein x equals approximately 0.036, y equals approximately 0.064, and 2: equals approximately 0.10.

OTHER REFERENCES Kroger: Some Aspects of the Luminescence of Solids, 1948, pages 292 and 297.

TOBIAS E. LEVOW, Primary Examiner R. D. EDMONDS, Assistant Examiner 

